Impellers are rotating components of a turbo machine that impart energy to, or harness energy from, a stream of fluid directed through the machine. For instance, an impeller used in a gas compressor may impart energy to a flow of air flowing through the impeller, and an impeller used in the turbine section may rotate a shaft connected thereto, due to the kinetic energy of hot gases passing over the impeller. These hot gases may be produced by combusting a hydrocarbon based fuel in a combustion chamber of the turbine engine. “Open faced impellers” may have a hub with a plurality of protruding blades. The shape of the blades may be configured to direct a flow of fluid between them. The hub may include a passageway for passing a drive shaft through. In some applications, a shrouded impeller may be preferred to an open faced impeller described above. A shrouded impeller is an open faced impeller with a circumferential shroud connecting the outer ends of the blades to define a cavity through which a flow of fluid is directed.
Conventional methods of construction of shrouded impellers include casting and machining. In a method involving casting, a shrouded impeller may, for example, be cast in a mold and finished by polishing to a required surface finish. In a method involving machining, the shrouded impeller may be created using any conventional machining operation. Shrouded impellers may also be formed from pre-fabricated open faced impellers. In this process, an open faced impeller formed by conventional forging, casting, or machining techniques, may be joined (welded, brazed, etc.) with a separately fabricated shroud. In such a construction, the joints connecting the shroud to the open faced impeller may be subject to failure due to the stresses induced during operation. To prevent these potential failures, shrouded impellers of a unitary construction have been created by machining.
U.S. Pat. No. 5,438,755 issued to Gilberson ('755 patent) describes a method of making a shrouded impeller of a unitary construction using three-dimensional CNC milling. The method of the '755 patent involves fabricating a shrouded impeller from a single blank using four machining steps. These steps include: turning and boring a rough forging to an impeller profile; removing material from the passageways of the impeller using a three-dimensional CNC milling machine; removing material in direct line of sight from the outside diameter of the impeller; and forming a hole through a central zone of each impeller passageway by three dimensional planning. Although the method of fabrication described in the '755 patent produces shrouded impellers of unitary construction, the method of the '755 patent may have drawbacks. For instance, machining blades and passageways in the presence of the shroud may be difficult or not possible, and therefore, expensive. The present disclosure is directed to solving one or more of the problems set forth above.